1. Field of the Invention
The present invention relates to a semiconductor device fabricating method, and more particularly, to a method for fabricating a capacitor of a semiconductor device for reducing leakage current between a dielectric film and an electrode.
2. Description of the Related Art
Capacitance (C) of a capacitor in a semiconductor device is expressed by the following Equation 1. ##EQU1##
Here, .epsilon..sub.0 denotes permittivity in a free space, .di-elect cons..sub.r denotes a dielectric constant of the particular dielectric film used, A denotes an effective area of an electrode, and d denotes the thickness of the dielectric film. As can be seen from Equation 1, capacitance is increased by changing three variables, i.e., the dielectric constant of the dielectric film, the effective area of a capacitor, and the thickness of the dielectric film.
Each of these methods for increasing the capacitance has its drawbacks. When a material having a large dielectric constant is used in a dielectric film to increase the capacitance of a capacitor, the energy band gap of the material is reduced, thereby increasing leakage current. The leakage current also increases if the thickness of the dielectric film is reduced.
Also, when a capacitor having a three-dimensional structure is fabricated to increase the effective area of the capacitor, the process thereof is complicated and the cost for the process increases.
As another drawback, a silicon dangling bond effect occurs at the interface between a silicon and a silicon oxide film in a transistor of a semiconductor device. The dangling bond forms an interface trap which operates as a trap level with respect to an electron. The interface trap affects the height of a Schottkey barrier, thus causing variation of a threshold voltage.
In the case of a capacitor, also, an interface trap exists between the electrode and the dielectric film which affects the height of the Schottkey barrier. Here, as the height of the barrier is lower, an electron passes more easily through the interface between the electrode and the dielectric film when a voltage is applied. As the dielectric film becomes thinner, the interface state between the electrode and the dielectric film has a significant influence. The height of this barrier has a direct effect on the leakage current depending on the interface state between the electrode of a capacitor and dielectric film.
Accordingly, the need exists for capacitors in semiconductor devices wherein leakage current is minimized.